Cell multiplexing apparatus handling multiple items of information

ABSTRACT

A cell multiplexing apparatus including call monitors and multiplexers. The call monitors monitor a plurality of channels for their call setting status and select at least two channels for their call setting status and select at least two channels for which the same cell may be assembled, i.e., for which the destination of the calls is the same. The multiplexers receive audio information or information already assembled in asynchronous transfer mode (ATM) cells from the channels selected by the call monitors, and disassemble and multiplex the received information for assembly into the payload of a new ATM cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a divisional of U.S. Ser. No. 08/835,995filed Apr. 11, 1997 now pending, which is a continuation of U.S. Ser.No. 08/510,121, filed Aug. 1, 1995, now abandoned, which is acontinuation of U.S. Ser. No. 08/004,134, filed Jan. 3, 1993, now U.S.Pat. No. 5,509,007, and claims priority to Japanese Application 4-5378filed Jan. 16, 1992 and Japanese Application 5-0363 filed Jan. 5, 1993,incorporated by reference herein. This application is also related toU.S. Ser. No. 09/467,759, filed Dec. 20, 1999.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to an asynchronous transfer mode(ATM) transmission apparatus for multiplexing coded audio signals into acell for transmission over a transmission network an ATM mode.

[0003] Research is progressing on the so-called ISDN (integratedservices digital network). This is a branch of technologies forconcurrently transmitting over a single network multiple pieces ofinformation that have different characteristics, such as audioinformation and dynamic image information. Drawing attention in thisarea presently is asynchronous transfer mode (ATM), a switchingtechnique indispensable for implementing a broadened ISDN (B-ISDN). Thistechnique involves dividing communication information into packetscalled cells of a fixed length for transmission.

[0004] The most commonly utilized method today for coding telephonevoice signals in digital format is pulse code modulation (PCM) at atransmission rate of 64 kilobits per second. Where it is desired tolower the transmission rate (also known as the bit rate) withoutdegrading the quality of voice transmitted, one known method employed isADPCM (adaptive differential pulse code modulation) at a transmissionrate of 32 kilobits per second.

[0005] About to be put into practice is what is known as low delay codeexcited linear prediction (LD-CELP:CCITT G728). This is a method forconverting every five values sampled at 8 kHz into a predetermined codeof 10 bits, whereby a transmission rate of 16 kilobits per second isprovided.

[0006] Where voice signals are transmitted as communication information,the quality of voice sound deteriorates if the transmission delay timeinvolved is prolonged. Thus there are strict limits as to how long thetransmission delay time is allowed to be.

[0007] Described below is a typical setup of the abovementioned ATMtransmission using voice signals. FIG. 2 is a block diagram of a typicalprior art ATM transmission apparatus, and FIG. 3 is a of an ATM cellused by the conventional apparatus of FIG. 2. In FIG. 2, an exchange 1accommodates subscriber lines from a plurality of subscriber terminals 2and is connected to the ATM transmission apparatus 4 via a plurality ofchannels 5.

[0008] Suppose that one of the subscriber terminals 2 (i.e., callingsubscriber) makes a call to communicate with another subscriber terminal(i.e., called subscriber) via an ATM transmission line 3. In that case,the exchange 1 first connects the terminal 2 of the calling subscriberto the ATM transmission apparatus 4 over a given channel 5.

[0009] In turn, the ATM transmission apparatus 4 converts into apredetermined digital code (called coded information) the voice signaltransmitted from the subscriber terminal 2 (calling subscriber) throughthe exchange 1 and channel 5. The ATM transmission apparatus 4 thengenerates an ATM cell 10, multiplexes it with another cell made of thevoice signal from the subscriber terminal 2, and transmits themultiplexed result over the ATM transmission line 3.

[0010] As depicted in FIG. 3, cells generated by the ATM transmissionapparatus 4 are each composed of 53 octets. The first five octetsconstitute an ATM header 7. The ATM header 7 includes a virtual pathidentifier (VPI) and a virtual channel identifier (VCI). The remaining48 octets make up a payload 8 comprising coded information.

[0011] Of the 48 octets constituting the payload, the first octetcontains a sequence number identifier (SN) and a data type identifier(IT), the last two octets make up an effective data length identifier(LI) and a cyclic redundancy check identifier (CRC). The remaining 45octets (i.e., 360 bits) constitute a payload user information part 11for transmitting the coded information.

[0012] The ATM transmission apparatus 4 of FIG. 2 is equipped for eachchannel 5 with a coder-decoder 41, a code buffer 42, a payload assembler43 and an ATM multiplexer 13. The channels 5 are provided commonly witha cross connection multiplexer 45. These components work as follows:

[0013] The coder-decoder 41 digitizes a voice signal illustrativelyaccording to the LD-CELP method. The voice signal has been transmittedfrom a subscriber terminal 2 (calling subscriber) over a channel 5 andthrough the exchange 1. The signal in digital format is stored in thecode buffer 42 downstream.

[0014] The payload assembler 43 monitors the amount of coded informationin the code buffer 42. On detecting an accumulation of 36 items of codedinformation (i.e., 360 bits, or 45 octets) in the code buffer 42, thepayload assembler 43 gets the accumulated 36 items of coded informationfrom the code buffer 42 and assembles them into a payload 8. The payload8 is then transferred to the ATM multiplexer 13 downstream.

[0015] Upon receipt of the payload 8 from the payload assembler 43, theATM multiplexer 13 composes a cell by adding an ATM header 7 to thepayload coming from the payload assembler 43. The cell when composed istransferred to the cross connection multiplexer 45.

[0016] The cross connection multiplexer 45 stores temporarily in a queue(i.e., buffer) the cells transferred from the ATM multiplexers 13upstream. The cells are then output onto the ATM transmission line 3 inthe order in which they were stored into the buffer.

[0017] As described, in the prior art ATM transmission apparatus 4, thecoded information made of the voice signals coming from subscriberterminals 2 is transmitted over the ATM transmission line 3 after 36items of the coded information are accumulated in the code buffer 42 andare assembled into a cell for transmission.

[0018] It takes 625 microseconds (μs) for the coder-decoder 41 togenerate one item of coded information (i.e., 125 μs×5). That is, adelay time of 22,500 μs occurs by the time 36 items of coded informationare accumulated in the code buffer 42 (i.e., 625 μs×36). This oftenmakes it difficult to comply with the time constraints on transmissiondelay under the LD-CELP method. As a result, a serious adverse effect onthe quality the transmitted voice may occur.

[0019] Presently, there is a possibility that in-house LAN's (local areanetworks), based on the DQDB (distributed queue dual bus) systemproposed under IEEE (Institute of Electrical and Electronics Engineers)802.6, will gain widespread acceptance. If that happens, the congestionof different types of communication information, which will affecttransmission, can be a severe disadvantage to the system.

[0020] Packet data transmitted over the LAN's have variable lengthswhile ATM cells 10 have a fixed length. When communication informationis divided, the divided items are multiplexed into an ATM cell 10. If afraction of the cell 10 constitutes the information, the remainingvacant parts are filled with dummy patterns so that the finished cellwill be a complete cell. The smaller the fraction and the higher thefrequency at which a fractionally complete cell occurs, the more dummypatterns are needed to fill the gap. As a result, the transmissionefficiency decreases.

[0021] More and more terminals connected to in-house LAN's includingthose in compliance with the DQDB system will likely be multi-mediaterminals such as TV telephone sets and audio/visual output devices.There is little doubt that the number of available channels will notkeep up with the growing number of multi-media terminals. Furthermore,if equipped with a transmitter-receiver for each different medium, themulti-media terminal will bloat in size and cost and will run counter totoday's trend toward downsized terminals with compact functions.

[0022] Certain kinds of communication information such as motionpictures require synchronism between dynamic image information and audioinformation when transmitted. Ensuring synchronism between the differentkinds of information is necessary so as to keep the received informationmeaningful. It may be arranged technically that each cell compriseseither audio or image information alone. In that case, a relativelysmall amount of audio information is in disproportionate contrast withlarge quantities of dynamic image information. This can result in whatis known as image cell drop-out, i.e., the rate of dynamic imageinformation transmission failing to keep up with the rate of audioinformation transmission. The image cell drop-out can be a major causeof deterioration in image quality.

SUMMARY OF THE INVENTION

[0023] It is therefore an object of the present invention provide a cellmultiplexing apparatus operating in asynchronous transfer mode (ATM),the apparatus minimizing the delay time required to transmitcommunication information of a single or a plurality of kinds over anATM transmission network while collectively handling communicationinformation of different media with no data drop-out.

[0024] In carrying out the invention and according to one aspectthereof, there is provided a cell multiplexing apparatus which receivescommunication information over at least two channels of any one of thesame and different kinds, and assembles the received information into anasynchronous transfer mode cell made of a fixed-length header and apayload, and which transmits the assembled cell. The apparatus comprisescall monitoring means for obtaining call setting information fromindividual items of the communication information and multiplexing meansfor multiplexing the communication information received over the minimumof two channels into a single asynchronous transfer mode cell of a fixedlength in accordance with the call setting information obtained by thecall monitoring means.

[0025] In a preferred structure according to the invention, themultiplexing means 200 may multiplex control and alarm information fromthe channels 5 selected by the call monitoring means together with, say,audio information into a cell. Alternatively, the multiplexing means 200may assemble a cell using audio signals obtained by converting aplurality of sampled values into a code of a predetermined number ofbits. Because the communication information 6 from the multiple channels5 is multiplexed, as described, into a single cell according to theinvention, the transfer delay is minimized.

[0026] When a plurality of items of information are multiplexed into asingle cell, the payload part of the cell may be formed to a fixed orvariable length. How the payload part is formed may be expressed aspayload control information that is prefixed to the beginning of thepayload 8.

[0027] The same kind of communication information (e.g., audioinformation) may be multiplexed into a single cell. Alternatively,communication information of different characteristics (audio and imageinformation) may be multiplexed into a single cell.

[0028] In a further preferred structure according to the invention, aplurality of ATM cells 10 received as communication information 6 may bedivided and the divided parts may be multiplexed into a new ATM cell 10.

[0029] These and other objects, features and advantages of the inventionwill become more apparent upon a reading of the following descriptionand appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a view illustrating the operating principle of thepresent invention;

[0031]FIG. 2 is a block diagram of a typical prior art ATM transmissionapparatus;

[0032]FIG. 3 is a view showing the constitution of an ATM cell used bythe conventional apparatus of FIG. 2;

[0033]FIG. 4 is a block diagram depicting the overall systemconfiguration of a first embodiment of the invention;

[0034]FIG. 5 is a block diagram of an ATM transmission apparatus in thefirst embodiment;

[0035]FIG. 6 is a view showing the format of an ATM cell used by thefirst embodiment;

[0036]FIG. 7 is a conceptual view indicating how data items aremultiplexed by the first embodiment;

[0037]FIG. 8 is a detailed view showing how call monitors areillustratively structured in the first embodiment;

[0038]FIG. 9 is a view depicting typical sequences of control operationsin effect when a call is connected by the first embodiment;

[0039]FIG. 10 is a view portraying the sequence of operations between acode buffer controller and a code buffer on the calling side where acall is connected by the first embodiment;

[0040]FIG. 11 is a view showing the sequence of operations between acode buffer controller and an ATM multiplexer on the called part where acall is connected by the first embodiment;

[0041]FIG. 12 is a view depicting the sequence of operations between acode buffer controller and a code buffer on the called side where a callis connected by the first embodiment;

[0042]FIG. 13 is a view illustrating the overall system configuration ofa second embodiment of the invention;

[0043]FIG. 14 is a function block diagram of a cell mapping part in thesecond embodiment;

[0044]FIG. 15 is a conceptual view showing how ATM cells are multiplexedby the second embodiment;

[0045]FIG. 16 is a view depicting the format of a channel identifier ina new ATM cell produced by the second embodiment;

[0046]FIG. 17 is a block diagram portraying the overall systemconfiguration of a third embodiment of the invention;

[0047]FIG. 18 is a view illustrating the format of a channel ID part ina new ATM cell produced by the third embodiment;

[0048]FIG. 19 is a block diagram depicting the overall systemconfiguration of a fourth embodiment of the invention;

[0049]FIG. 20 is a conceptual view showing how ATM cells are multiplexedby the fourth embodiment;

[0050]FIG. 21 is a block diagram sketching the overall systemconfiguration of a fifth embodiment of the invention;

[0051]FIG. 22 is a block diagram of an interface part that handles thetransmission and reception of ATM cells in the fifth embodiment;

[0052]FIG. 23 is a function block diagram showing how a buffercontroller and an ATM multiplexer operate on the transmitting side ofthe fifth embodiment;

[0053]FIG. 24 is a function block diagram depicting how a buffercontroller and an ATM multiplexer operate on the receiving side of thefifth embodiment;

[0054]FIG. 25 is a conceptual view illustrating how ATM cells aremultiplexed by the fifth embodiment;

[0055]FIG. 26 is a view showing typical contents of payload controlinformation parts in ATM cells in connection with the fifth embodiment;

[0056]FIG. 27 is a view describing how the ATM cells multiplexed by thefifth embodiment as shown in FIG. 25 are restored back to the originalinformation;

[0057]FIG. 28 is a view showing a detailed format of an ATM cell inconnection with the fifth embodiment;

[0058]FIG. 29 is a view indicating what is typically meant by a DBheader stored in a payload control information part in connection withthe fifth embodiment;

[0059]FIG. 30 is a view depicting typical contents of a DC header storedin a payload control information part in connection with the fifthembodiment; and

[0060]FIG. 31 is a view showing the format of an ATM cell that actuallycontains information in connection with the fifth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] In FIG. 1, call monitoring means 100 monitors each of themultiple channels 5 for the call setting status in order to select aplurality of channels 5 for which the same cell may be assembled (i.e.,for the same destination). The coder-decoder 41 for each channel 5converts to coded information the audio signal transmitted over thecorresponding channel 5. Cell multiplexing means 200 takes audioinformation or ATM cells from the multiple channels 5 selected by thecall monitoring means 100, through the coder-decoder 41, divides areceived information or ATM cells, and assembles the divided parts ina-multiplexing manner into a new cell (containing a payload 8). Thecross connection multiplexer 45 places in a queue the cells coming fromthe multiplexing means 200.

[0062] First Embodiment:

[0063] The first embodiment of the invention is arranged to divide audioinformation from plurality of channels into ATM cells 10 of a fixedlength each for multiplexing. FIG. 4 depicts the overall systemconfiguration of the first embodiment, FIG. 5 is a block diagram of anATM transmission apparatus in the first embodiment, and FIG. 6 shows theformat of an ATM cell used by the first embodiment.

[0064]FIG. 7 is a conceptual view indicating how data items aremultiplexed by the first embodiment. FIG. 7 shows how audio informationfrom a plurality of channels 5 (data A, data B, data C, . . . ) ismultiplexed into ATM cells 10.

[0065] In FIG. 4, an exchange 1 accommodating subscriber lines fromsubscriber terminals 2 is connected to an ATM transmission apparatus 4.The ATM transmission apparatus 4 on the calling side is in turnconnected via an ATM transmission line 3 to another ATM transmissionapparatus 4 on the called side.

[0066] In FIG. 5, call monitors 46 constituting call monitoring means 10are provided in the ATM transmission apparatus 4. The call monitors 46are respectively connected to ATM processors 44. Each ATM processor 44comprises coder-decoders 41, a data multiplexer 36 and an ATMmultiplexer 13, the latter two constituting multiplexing means 200.

[0067] Referring again to FIG. 4, suppose that a subscriber (callingsubscriber) wishes to make a call to another subscriber (calledsubscriber). In that case, the exchange 1 connects the callingsubscriber's terminal 2 to the ATM transmission apparatus 4 via a givenchannel 5. In FIG. 5, the calling subscriber sends to the ATMtransmission apparatus 4 call setting information for setting up thecall.

[0068] In the ATM transmission apparatus 4, the call monitor 46 monitorsthe call setting information coming from calling subscribers over thechannels (data A-n). From the call setting information, each callmonitor 46 obtains the settings needed to determine a virtual pathidentifier VPI and a virtual channel identifier VCI for the relevant ATMprocessor 44. The settings are transferred along with identificationinformation of each channel 5 to the data multiplexer 36. The transferis made to a buffer controller 12 (buffer control means 12) in the datamultiplexer 36 via a control line 37 provided independently the datacommunication lines.

[0069] How each call monitor is typically structured will now bedescribed with reference to FIG. 8. As shown in FIG. 8, each callmonitor comprises call monitor units 38 provided for the respectivechannels, a control signal transmitter-receiver 15 for recognizing achannel control signal received over the channels 5, and a transmissionpath selector 16 for obtaining path information from the channel controlsignal.

[0070] The control information including the channel control informationmay be obtained on an in-slot basis (i.e., the information is containedin the audio signal from the channels 5), or on an out-slot basis (theinformation is received over a separate control line 37 independent ofthe audio information).

[0071] In the data multiplexer 36 of FIG. 5, the buffer controller 12analyzes the information sent from the call monitor 46, determines thevirtual path identifier VPI and virtual channel identifier VCI foridentifying the call, selects up to six channels 5 that determined theidentifiers VPI and VCI, and forms a group of communication dataaccordingly. This group of communication data is a group which comprisescommunication information received over different channels 5 and whichcomplies with the virtual path identifier VPI and virtual channelidentifier VCI of the next stage.

[0072] When the calling subscriber starts transmitting communicationinformation (audio signal in this example), the coder-decoder 41provided for each channel 5 converts to coded information the audiosignal transmitted over the corresponding channel 5 and through theexchange 1. The conversion is carried out on the basis of the LD-CELPmethod. The coded information is accumulated in the code buffer 42 ofthe data multiplexer 36.

[0073] The buffer controller 12 monitors the amount of coded informationbeing accumulated in each code buffer 42. A point is eventually reachedwhere the buffer controller 12 finds that the code buffers 42corresponding to the six channels 5 forming the same group have eachaccumulated five sets of coded information (a total of 50 bits). At thatpoint, the buffer controller 12 obtains the accumulated five sets ofcoded information from the buffers and stores them into a userinformation part 11 of each channel 5 in the payload 8 of the cell shownin FIG. 6.

[0074] In addition, the buffer controller 12 collects through the callmonitor 46 the control information on the connection status of sixsubscribers forming the same group (e.g., on-hook/off-hook information)as well as alarm information in connection therewith. The collectedinformation is stored in a 10-bit control/alarm information areaassigned each of the six channels 5 in the payload 8.

[0075] Five sets of coded information (a total of 50 bits) andcontrol/alarm information (10 bits) are allocated to the six channels 5.These sets of coded information constitute part of the 360-bit payload8.

[0076] In the setup of FIG. 6, each coded information area of thepayload 8 is formed to a fixed length (50 bits). Alternatively, theseinformation areas may be formed to a variable length each. How this canbe achieved will be described later in connection with the fifthembodiment (FIG. 25).

[0077] The payload 8 is assembled under control of the buffer controller12. The payload data are then output to the ATM multiplexer 13 inaccordance with the virtual path identifier VPI and virtual channelidentifier VCI determined commonly for those channels 5 constituting thesame group.

[0078] The ATM multiplexer 13 assembles a cell by supplementing thepayload 8 from the upstream multiplexing part with an ATM header 7containing the virtual path identifier VPI and virtual channelidentifier VCI. The assembled cell is transmitted to a cross connectionmultiplexer 45. The cross connection multiplexer 45 places in a queue(i.e., buffer) the cells coming from various ATM multiplexers 13. Thesecells are then output over the ATM transmission line 3 in the order inwhich they arrived.

[0079] Described below with reference to FIGS. 9 through 12 are thesequences of control operations in effect when a call is made by thefirst embodiment. In FIG. 9, the upper half shows the sequence ofcontrol operations on the calling side of the ATM transmission apparatus4, and the lower half indicates the sequence of control operations onthe called side of the ATM transmission apparatus 4.

[0080] On the calling side of the ATM transmission apparatus 4, as shownin the upper part of FIG. 9, the control signal transmitter-receiver 15in the call monitor 46 receives call information, i.e., a start signaland a selection signal, from a calling subscriber's terminal 2 belongingto the same exchange I. At that point, the control signaltransmitter-receiver 15 extracts a channel control signal from thereceived information and sends the signal to the transmission pathselector 16.

[0081] Based on the channel control signal received, the transmissionpath selector 16 selects an appropriate transmission path, generateschannel path information, and sends the information to the code buffercontroller 12. In turn, the code buffer controller 12 determines thepath of an ATM cell to be generated on the basis of the channel pathinformation. With the cell path determined, the code buffer controller12 sends cell transmission path information to the ATM multiplexer 13.

[0082] Concurrently, the code buffer controller 12 reads codedinformation from the code buffer 42. If any of the channels involved isbusy with a call, the code buffer controller 12 notifies the ATMmultiplexer 13 with only the control signal such as cell transmissionpath information until an acknowledge signal is received from theopposite exchange. It is only after the opposite exchange 1 acknowledgesreceipt and completion of the call and its connection that the codedinformation is transmitted to the ATM multiplexer 13.

[0083]FIG. 10 portrays the sequence of operations performed between thecode buffer controller 12 and the code buffer 42 in the above setup. Asdescribed, upon receipt of the channel path information from thetransmission path selector 16, the code buffer controller 12 determinesthe cell path and makes a read request to the code buffer 42 bydesignating an appropriate address thereto. The coded information isread from the code buffer 42 in response to the read request and istransferred to the code buffer controller 12. When one cell of codedinformation has been read out by the code buffer controller 12, thecontroller 12 outputs a cell generation complete notice to the ATMmultiplexer 13. The cell generation complete notice prompts the ATMmultiplexer 13 to make a read request. In turn, the code buffercontroller 12 supplies the ATM multiplexer 13 with payload informationmade of the channel control signal and of the coded information.

[0084] When the ATM multiplexer 13 prefixes the header 7 to the payloadinformation, the result is an ATM cell 10 that is transferred throughthe cross connection multiplexer 45 of FIG. 5 and on to the ATMtransmission line 3.

[0085]FIG. 11 shows the sequence of operations in effect when callinformation sent from the ATM transmission apparatus 4 on the callingside is received as the ATM cell 10 by the ATM transmission apparatus 4on the receiving side. Upon receipt of the ATM cell 10, the ATMmultiplexer 13 sends a cell receipt acknowledge signal to the codebuffer controller 12 within the receiving-side ATM transmissionapparatus 4. In turn, the code buffer controller 12 makes a read requestto the ATM multiplexer 13. The read request prompts the ATM multiplexer13 to read the payload information (coded and control information) fromthe ATM cell 10. The code buffer controller decodes the channel path andthe decoded channel path information is sent by the code buffercontroller 12 to the control signal transmitter receiver 15. The channelpath information received by the control signal transmitter-receiver 15is sent both to the call monitor units 38 (FIG. 8) and to thetransmission path selector 16.

[0086] In parallel with the above process, the code buffer controller 12writes the coded information to the code buffer 42. The sequence of thewrite operation is shown in FIG. 12. Specifically, upon receipt of thepath information from the transmission path selector 16, the code buffercontroller 12 decodes the channel path and makes a write request to thecode buffer 42. When the code buffer 42 grants permission to write, thecode buffer controller 12 writes to the code buffer 42 the codedinformation obtained from the payload 8 in the ATM cell 10. Subsequentoperations, not shown in FIG. 12, include outputting the codedinformation that came from the code buffer 42 onto the ATM transmissionline 3 and transmitting the information to the called subscriber'sterminal.

[0087] The lower half of FIG. 9 depicts the sequence of operationsperformed by the ATM transmission apparatus 4 on the called side whenthe call is acknowledged by the called subscriber. Specifically, whenthe called-side ATM transmission apparatus 4 receives acknowledgeinformation (acknowledge signal) from the called subscriber, a callconnection signal is extracted by the control signaltransmitter-receiver 15 from the received information and is sent to thecode buffer controller 12 via the transmission path selector 16. Then inthe same sequence as shown in FIG. 10, the coded information is readfrom the code buffer 42 for cell generation. The payload information isforwarded to the ATM cell multiplexer 13.

[0088] The ATM multiplexer 13 prefixes the header 7 to the payloadinformation. The payload information prefixed with the header 7 is sentto the cross connection multiplexer 45. In turn, the cross connectionmultiplexer 45 transmits the acknowledge information as an ATM cell 10to the ATM transmission apparatus 4 on the calling side.

[0089] As described, the first embodiment works roughly as follows: whenthe code buffers 42 corresponding to the six calls that share a virtualpath identifier VPI and a virtual channel identifier VCI have eachaccumulated five sets of coded information, the data multiplexer 36(buffer controller 12) in the ATM transmission apparatus 4 startsassembling one set of payload information using separately collectedcontrol and alarm information. At this point, it takes 3,125 μs (i.e.,625×5) for each of the code buffers 42 to accumulate five sets of codedinformation. That is, the coded information accumulation time with thecode buffers 42 is reduced to 5/36 of the time normally calculated withthe prior art ATM transmission apparatus 4 (22,500 μs).

[0090] Second Embodiment:

[0091] The second embodiment is arranged to further multiplex ATM cells10 into a new ATM cell 10 through remapping in an ATM node (i.e., ATMtransmission apparatus 4), the new ATM cell being output onto the ATMtransmission line 3. Among the plurality of ATM cells 10 to bemultiplexed, the VCI value of a given ATM cell 10 is taken as the VCIvalue of the header 7 for the new ATM cell 10. The VCI values of the oldATM cells 10 are stored as channel identification information in thepayload 8 of the new ATM cell 10.

[0092] As depicted in FIG. 13, the system configuration of the ATMtransmission apparatus 4 in the second embodiment includes ATMconverters (AAL's) and a path distributor 50. The path distributor 50contains a path identifier 17 and a cell mapping part 18, the pathidentifier operating as the call monitoring means 100. FIG. 4 is afunction block diagram of the cell mapping part 18. The cell mappingpart 18 comprises a cell mapping controller 22, a timer 20 controlled bythe cell mapping controller 22, a mapping buffer 32, a VCI detector 21and a cell output part 52.

[0093] What characterizes the second embodiment is that the signals fromsubscriber terminals 2 are converted by the ATM converters (AAL's) intoATM cells which are then remapped by the path distributor 50 into anewly multiplexed ATM cell 10 for output.

[0094] In FIG. 13, the path identifier 17 acts as a kind of selector.While receiving information in the form of ATM cells 10 from the ATMconverters (AAL's), the path identifier 17 detects VPI values from thesecells. If ATM cells 10 found destined to the same path based on VPIdetection are received within a predetermined period of time, the pathidentifier 17 inputs these ATM cells into the cell mapping part 18. InFIG. 15, cells #1 and #2 have the same VPI value.

[0095] When a first ATM cell 10 (i.e., first cell #1 given after timerreset) arrives from an ATM converter (AAL), the timer 20 is activatedand the VCI detector 21 is fed with a pulse signal indicating the inputof the first ATM cell 10 (cell #1). The VCI detector 21 detects the VCIvalue from the cell, and notifies the cell mapping controller 22 of theVCI value of the first ATM cell 10 (cell #1).

[0096] The cell mapping controller 22 then assembles a new ATM cell 10(cell #A) with its VCI value taken from the first ATM cell 10 (cell #1).That VCI value is also stored in a channel ID part 24 of the payload 8.

[0097] When the path identifier 17 detects the arrival of an ATM cell(cell #2) having the same VPI value as that of the first cell beforetime is up on the timer 20, the VCI detector 21 reads the VCI value fromthe header 7 of the ATM cell 10 (cell #2). The cell mapping controller22 writes the VCI value of the ATM cell (cell #2) only to the channel IDpart 24 in a payload control information part 23 of the payload 8.Thereafter, whenever an ATM cell 10 is input of which the VPI value isthe same as the above, the VCI value is stored successively into thechannel ID part 24 of the payload 8. The successive storage of VCIvalues into the channel ID part 24 continues until a timeout is reachedon the timer 20.

[0098] Concurrently with the storage of the VCI values, the informationon the ATM cells 10 (cells #1, #2, etc.) is stored consecutively into auser information part 11 of the payload 8.

[0099]FIG. 15 illustrates how ATM cells (cells #1, #2, etc.) are relatedin format to the new ATM cell (cell #A) in connection with the secondembodiment. As shown, the VPI and VCI values of the first ATM cell (cell#1) are adopted as those of the new ATM cell 10 (cell #A). The VCIinformation of the second and subsequent ATM cells is storedsuccessively into the channel ID part 24. The control information anduser information of the ATM cells 10 are placed for each channel intoareas of a fixed length each within the user information part 11 of thepayload 8 in the new ATM cell 10 (cell #A).

[0100] The channel ID part 24 accommodates, in addition to the VCIvalues of the ATM cells 10 (cells #1, #2, etc.), data length informationindicating the amount of information (significant bit count or bytelength) of each old ATM cell 10. If the control information is the sameor common to the channels 5, the information may alternatively bewritten to an appropriate address of the new ATM cell 10 (cell #A).Where one sampled data item is fixed to a data length of eight bits, aswith 64-kbps PCM audio information, the data length information may bestored as a single item or may be omitted altogether.

[0101] When a predetermined period of time has elapsed on the timer 20(i.e., upon time-out), the timer 20 outputs a trigger signal to the celloutput part 52 through the cell mapping controller 22. With the triggersignal output, the VPI value is written to the header 7 of the new ATMcell 10 (cell #A) via the cell output part 52. The ATM cell 10 (cell #A)is then output onto the transmission line.

[0102] Even before the time-out of the timer 20, the cell mapping part18 outputs the trigger signal to the cell output part 52 if the userinformation part 11 of the ATM cell 10 (cell #A) has been filled tocapacity with information. This prompts the output of the ATM cell 10(cell #A). At this point, the timer 20 is reset regardless of thetime-out that may or may not be reached on the timer.

[0103] In the receiving side ATM node, the old VCI values of the old ATMcells (cells #1, #2, etc.) are extracted from the channel ID part 24 inthe payload 8 of the new ATM cell 10 (cell #A). At the same time, thedata length information is read out to determine the allocation of theinformation for the respective old cells. The operations combine toreassemble the old ATM cells 10 (cells #1, #2, etc.).

[0104] Although the above setup involves storing the VCI value of thefirst ATM cell (cell #1) in the channel ID part 24 of the payload 8, thechannel ID part 24 may alternatively accommodate the VCI values of thesecond and subsequent ATM cells 10 (from cell #2 on). In the lattercase, the VCI value in the header 7 of the ATM cell 10 (cell #A) thathas arrived may be used unchanged as the first user information on thereceiving side.

[0105] Although the above setup uses the VCI value of the first ATM cell10 (cell #1) as the VCI value of the new ATM cell 10 (cell #A), analternative arrangement may be employed. Specifically, the maximum orminimum VCI value of the old ATM cells 10 (cells #1, #2, etc.) may bedetected by the VCI detector 21. Then the cell mapping part 18 may writethe maximum or minimum VCI value to the header 7 of the new ATM cell 10(cell #A). In this case, the writing of the VCI value to the header 7 ofthe new ATM cell 10 (cell #A) is accomplished after mapping.

[0106] As described, the second embodiment assembles old ATM cells 10(#1, #2, etc.) regardless of their many dummy patterns (see FIG. 15)into a new ATM cell (#A) with no dummy pattern. In this manner, thepayload 8 of the new ATM cell 10 is utilized efficiently. Because theassembly of the new ATM cell 10 is monitored by the timer 20, there isno delay in the output of that cell.

[0107]FIG. 16 depicts the format of a channel ID part in a new ATM cell(#A) produced by a variation of the second embodiment. One way toapportion VPI and VCI values of ATM cells in the channel ID format is toset low-order n bits as per the number of paths or channels needed bythe user while the high-order bits are fixed (e.g., all bits fixed tozero). In the example of FIG. 16, the channel ID part 24 of the new ATMcell 10 (#A) accommodates only the low-order n bits and VCI significantbit count of the VCI values from the old ATM cells 10 (#1, #2, etc.).

[0108] According to the preceding method, three bits are enough when itcomes to expressing, say, five channels for use by a single path (VPI).Even if the use of “000” is prohibited by the user, a three-bit formatprovides expressions of up to seven channels (001-111).

[0109] Where the above method is employed, the cell mapping part 22takes the significant bit count n (n=7 in the above example) of the VCIvalues from the input ATM cells 10 (#1, #2, etc.) and stores the countinto a significant bit count storage part of the channel ID part 24 inthe payload 8. Following the bit count storage part, the cell mappingpart 22 stores consecutively the low-order n bits of the VCI values fromthe input ATM cells 10.

[0110] The value n may be determined in one of two ways: either it isset when entered initially through the network, or it is determined asneeded based on the information obtained from the VCI detector 21. Inany case, the format of FIG. 16 allows the channel ID part 24 to be usedefficiently so that an extensive user information part 11 will besecured in the payload 8.

[0111] Third Embodiment:

[0112] In the third embodiment, an ATM node (i.e., ATM transmissionapparatus 4) further multiplexes the information in the form of ATMcells 10 into a new ATM cell 10 through remapping, and outputs the newATM cell to another ATM node. Among the plurality of ATM cells 10 to bemultiplexed, the VCI value of a given ATM cell 10 is taken as the VCIvalue of the header 7 for the new ATM cell 10. The VCI values of the oldATM cells 10 are converted to channel numbers through a management table25 for storage into the channel ID part 24 of the new ATM cell 10.

[0113]FIG. 17 portrays the system configuration of the third embodiment.In FIG. 17, the cell mapping controller 22 is basically the same incomposition as that of the second embodiment except for the managementtable 25 shown in the figure. The other components that are functionallyidentical to those described in connection with the second embodimentare designated by the same reference numerals, and any repetitivedescription thereof is omitted. As depicted in FIG. 17, the managementtable 25 is made of conversion tables each converting the VCI numbersunder a given VPI into channel numbers.

[0114] When notified of the VCI values of the old ATM cells 10 (#1, #2,etc.) by the VCI detector 21, the cell mapping controller 22 referencesthe conversion table of the applicable VPI in the VCI management table25, and reads the corresponding channel numbers therefrom. The channelnumbers thus read out are written consecutively, together with datalength information, to the channel ID part 24 of the new ATM cell 10(#A).

[0115]FIG. 18 illustrates the format of the channel ID part 24 in a newATM cell produced by the third embodiment. As with the secondembodiment, if the data length is the same throughout the payload userinformation part 11 of this format, only one data length may be stored,or the storage of data lengths may be omitted altogether.

[0116] Fourth Embodiment:

[0117] In the fourth embodiment, an ATM node (i.e., ATM transmissionapparatus 4) further multiplexes the information in the form of ATMcells 10 into a new ATM cell 10 through remapping, and outputs the newATM cell to another ATM node. What characterizes the fourth embodimentis that a representative VCI indicating a plurality of multiplexed cellsis stored as the VCI value of the new ATM cell 10.

[0118]FIG. 19 depicts the system configuration of the fourth embodimentwhich includes a representative VCI prefixing part 53. The othercomponents that are functionally identical to those described inconnection with the second embodiment are designated by the samereference numerals, and any repetitive description thereof is omitted.

[0119] With the fourth embodiment, the cell mapping controller 22 sendsa trigger signal to the representative VCI prefixing part 53 immediatelyafter reset or time-out of the timer 20 or when the user informationpart 11 of the payload 8 has been filled with information. This causesthe representative VCI value to be written to the header 7 of the newATM cell 10 (#A). The representative VCI stands for a plurality of cellsbeing multiplexed and is preferably reserved as a special number. FIG.20 shows how old ATM cells 10 (#1, #2, etc.) compare in format with thenew ATM cell 10 (#A) in connection with the fourth embodiment.

[0120] Upon receipt of the multiplexed ATM cell 10 (#A) prefixed withthe representative VCI, the ATM node on the receiving side disassemblesthe ATM cell 10 (#A) into the original plurality of ATM cells 10 (#1,#2, etc.). The disassembled ATM cells 10 are transferred to theterminals corresponding thereto. If an ATM cell 10 (#B) has norepresentative VCI prefixed thereto, the cell is transferred intact tothe corresponding terminal or ATM transmission apparatus 4.

[0121] The prefixing of the representative VCI may be implemented bycombining the methods of the second and third embodiments.

[0122] Fifth Embodiment:

[0123] The fifth embodiment involves dividing into variable lengths aplurality of items of information generated by terminals (i.e., terminalequipment; TE) in an in-house setup and multiplexing these items in thepayload 8 of an ATM cell 10.

[0124]FIG. 21 sketches the overall system configuration of the fifthembodiment. In the in-house setup of FIG. 21, terminals 31 (TE)connected to in-house bus means 28 coming from network transit switchingequipment 26 are illustratively multimedia terminals. Each of theseterminals incorporates a pair of interface parts 30 (See FIG. 22) thattransmit and receive image information, audio information, text data andother data in the form of ATM cells 10. FIG. 22 illustrates an interfacepart 30 in more detail. As depicted, the interface part 30 comprises anATM multiplexer 13, a buffer controller 12 and a buffer 54. In eachterminal (TE), one interface part 30 is located on the upward-bound busside and the other interface part 30 on the downward-bound bus side.

[0125]FIG. 23 is a function block diagram showing how the buffercontroller 12 and the ATM multiplexer 13 operate on the transmittingside of the fifth embodiment, and FIG. 24 is a function block diagramdepicting how the same components operate on the receiving side.

[0126] What takes place on the transmitting side of the fifth embodimentin FIG. 23 is as follows: data items (A, B, C, . . . , N) from terminalsare first written to the buffer 54. When a buffer input counter 2302 hascounted written data of each of the data items up to a predeterminedvalue, the counter notifies an input transmission rate calculation part2303 that the predetermined count value of one of the data items isreached. Based on that input count value, the input transmission ratecalculation part 2303 calculates the transmission rate of the input dataof the one and notifies a payload assembly ratio calculation part 2305of that rate. At the same time, a desired transmission rate requestprocessing part 2304 receives desired transmission rate requests fromthe terminals (TE) and notifies the payload assembly ratio calculationpart 2305 of these requests.

[0127] Based on the received information on the data from a busmonitoring and processing part 2312, the payload assembly rationcalculation part 2305 determines how the different data items are to beallocated in the payload 8. The data allocation thus determined is sentto a sub-header assembly part 2309 and to a read order and amountcontroller 2306 of the payload control information part 23.

[0128] In turn, the read order and amount controller 2306 activatesindividual input buffer reading part 2307 which reads necessary amountsof data from the buffer 54 in a predetermined order. The read-out dataare handed over to a payload data assembly part 2308 of the ATMmultiplexer 13.

[0129] After the sub-header assembly part 2309 prefixes the payloadcontrol information part 23 as a sub-header 7 to the payload 8, an ATMheader prefixing part 2310 prefixes the other items of the header 7(e.g., VPI, VCI) to the ATM cell 10. The completed ATM cell 10 is thensent to a transmission buffer 2311 (first-in first-out memory) in theATM multiplexer 13. From the buffer 2311, the ATM cell 10 is output ontothe in-house bus means 28.

[0130] What takes place on the receiving side of the fifth embodiment inFIG. 24 is as follows: when an ATM cell 10 is received through thein-house bus means 28 (FIGS. 21 and 22), cell receipt information issent from an ATM header Identification part 2413 to a bus monitoring andprocessing part 2412 within the ATM multiplexer 13. This causesnecessary processing to take place according to the protocol (e.g., DQDBprotocol) of the in-house bus means 28.

[0131] The ATM cell thus received is accumulated in a reception buffer2414 (first-in first-out memory) in the ATM multiplexer 13. Thereafter,the ATM cell is sent both to a sub-header removal part 2416 and to asub-header analysis part 2415, the latter analyzing the sub-header 7held in the payload control information part 23. In accordance with theresult of the analysis on the sub-header 7, the payload controlinformation part 23 is removed and the user information part 11 of thepayload 8 is disassembled by a payload data disassembly part 2417.Following disassembly, image information, audio information, text dataand other data are transferred to individual data transmission bufferwriting parts 2419 via individual data buffers 2418 (first-in first-outmemory). These kinds of information are read from the buffers accordingto the transmission rate determined by a desired transmission raterequest processing part 2421.

[0132] What characterizes the fifth embodiment is that, as discussed,with reference to FIG. 23, the relative ratio at which to assembledifferent data into the payload 8 is varied (by the payload assemblyratio calculation part 2305) in accordance with the desired transmissionrates requested and with the actually input transmission rate. While thefirst through the fourth embodiment allocate data in a fixed lengthformat within the payload 8 upon multiplexing of information in the ATMcell 10, the fifth embodiment allocates data in a variable length formatwithin the payload 8.

[0133]FIG. 25 is a conceptual view illustrating how ATM cells aremultiplexed by the fifth embodiment. In FIG. 25, transmitted informationcomposed of four data types (data A through data D in the upper part ofthe figure) is a shown multiplexed in variable lengths (in the lowerpart of the figure) within the payload 8 of an ATM cell 10. These fourkinds of data (data A-D) may be data for a different channel each (e.g.,data A representing image, data B sound, data C text data). The fifthembodiment is particularly effective when used with an in-house setupwherein multimedia terminals connected to an in-house LAN are oftenrequired to transmit and receive information of different channels insynchronism.

[0134] Generally, the ATM cell 10 comprises the ATM header 7, payloadcontrol information part 23 and payload user information part 11. Theratio of assembling each of different types of information into thepayload user information part 11 is calculated by the payload assemblyratio calculation part 2305. The ratio is determined after considerationof such factors as whether or not the information to be transmittedneeds to be processed at high speed and whether or not the informationis to be handled on a burst basis.

[0135]FIG. 26 shows typical contents of payload control informationparts in ATM cells (i.e., lower half of what is depicted in FIG. 25) inconnection with the fifth embodiment, and FIG. 28 gives a detailedformat of one of such ATM cells. As illustrated in FIG. 28, the payloadcontrol information part 23 contains a DB header (first control area 34)and a DC header (second control area 35). The DB header comprisesidentifiers each indicating the beginning, an intermediate portion orthe end of the information in question. The DC header includesidentifiers indicating the data length of each item of information heldin this ATM cell 10.

[0136] Take, for example, the first ATM cell 10 (cell 1) shown in thelower half of FIG. 25. This ATM cell contains the beginning of each ofdata A through data C, while data D is not stored. Thus the DB headercontains an identifier (e.g., “01”) indicating the beginning of each ofdata A through data C, and includes another identifier (e.g., “00”)indicating the absence of data D (see FIG. 29, to be discussed later).The DC header stores the data length of each of the different data (Al,B1, C1; see FIG. 30, to be discussed later).

[0137] On the receiving side, the DB and DC headers are read out of thepayload control information part 23. The information contained in theheaders allows the receiving side ATM transmission apparatus torecognize what kinds of information are held and how they are allocatedin the payload user information part 11 of the ATM cell 10 in question.With the necessary information thus revealed, the original data Athrough D are restored precisely. FIG. 27 describes how the ATM cellsmultiplexed by the fifth embodiment as shown in the lower half of FIG.25 are restored back to the original data (data A through D).

[0138] In the ATM cell format shown in FIG. 28, what characterizes thefifth embodiment is that, as mentioned above, the payload userinformation part 11 is headed by the payload control information part 23which comprises the first control area 34 and second control area 35.The first and the second control areas 34 and 35 accommodate the DBheader and DC header, respectively, as identifiers. The DB header maystore up to four, two bits in length each. The meanings of theseidentifiers (DCF's) are listed in FIG. 29.

[0139] In FIG. 29, a bit string “00” held in-a DCF means that no data isstored in the corresponding payload user information part 11, a bitstring “01” means that the beginning of transmitted data is stored; abit string “10” means that an intermediate portion of the transmitteddata is stored, and a bit string “11” means that the end of thetransmitted data is stored.

[0140] The DC header may contain up to four pairs of identifiers, eachpair indicating a data length (DL) and a data sequence (DSN, or datasequence number). The DL identifier denotes the length of thecorresponding data accommodated in the payload user information part 11(to be described below), and the DSN identifier designates the datasequence number of the applicable data as counted from the first data.

[0141] The payload user information part 11 ranges from the eleventhoctet to the fifty-second octet. Actual data are allocated in this partaccording to the ratio determined for the respective data. FIG. 31 showsthe format of an ATM cell that contains actual data in connection withthe fifth embodiment.

[0142] As described and according to the fifth embodiment, numerouskinds of data are multiplexed in each ATM cell 10 in which the payload 8is apportioned in variable lengths. This feature boosts the efficiencyof data transmission and makes effective use of the available trafficcapacity thanks to the high concentration of transmitted data.

[0143] Because there is no need to classify data types on a network 27(in FIG. 21), the structure of the network can be simplified.

[0144] With no need to change transmission and reception protocols onany terminal (TE) for each different type of data to be transmitted inan in-house setup, the terminal may be made smaller in size and simplerin structure than before.

[0145] Since it is not necessary to repeat call settings for each set ofdata to be transmitted, the call setting procedure becomes moreefficient. As a result, transmission costs are reduced.

[0146] The ease of keeping synchronism between a plurality of kinds ofdata for simultaneous transmission contributes to preventing the voiceor image drop-out during multimedia information transmission.

[0147] As many apparently different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that the invention is not limited to the specific embodimentsthereof except as defined in the appended claims.

What is claimed is:
 1. A cell multiplexing apparatus for receivingcommunication information over a minimum of two channels and fortransmitting the communication information to a transmission line, saidcell multiplexing apparatus comprising: call monitoring means forobtaining call setting information from said communication, indicativeof monitor control information for each channel; and at least onemultiplexing means, each of said at least one multiplexing means formultiplexing said communication information received over said minimumof two channels into a single cell of a fixed length comprising a headerand a payload, having recognize information to recognize each channeland length of the communication information, in accordance with saidcall setting information obtained by said cell monitoring means, andtransmitting said single cell to the transmission line.